Press jacket and use thereof, and press roll and shoe press

ABSTRACT

A press cover or jacket includes at least a first and a second polymer layer. The first polymer layer is a radially outermost polymer layer as seen relative to the longitudinal axis of the press cover and has a thickness that is at most 60% of the overall thickness of the press cover as seen in the radial direction of the press cover. The first polymer layer includes grooves or holes which are incorporated in the radially outermost lateral surface thereof and the depth of the grooves or holes, as seen in the radial direction of the press cover, have a depth that corresponds at most to 95% of the thickness of the first polymer layer. A press roll, a shoe press and a method of using a press cover are also provided.

The invention proceeds from a press cover, especially for a press apparatus for treatment of a fibrous material layer, for example for smoothing or dewatering thereof, with specifics according to the independent claims. The invention also relates to a press roll, to a shoe press and to the use of a press cover in such a press roll, with specifics according to the further independent claims.

Press apparatuses such as shoe presses have long been part of modern papermaking machines. They essentially comprise a shoe in a stationary arrangement (also called press shoe) that extends in a machine cross direction, and a circumferential press cover around the stationary shoe. The press cover is deformable and takes on essentially a tubular shape in operation. The shoe is formed such that it forms a press nip (press gap) with an opposing roll. The press nip is defined by the contact area of the opposing roll in the shoe. The shoe is designed to be movable and can be moved against the opposing roll.

Enormous demands are placed on the press cover in relation to its stability, namely with regard to surface hardness, and resistance to pressure, temperature and hydrolysis. The press cover is additionally exposed to significant flexural cycling stresses during operation. On arrival at the edge of the shoe—upstream of the press nip viewed in rotation direction of the press cover—there is initially flexion with a comparatively small radius. This immediately becomes an opposing flexion on passage through the press nip. On exit at the other edge of the shoe, i.e. downstream of the press nip viewed in rotation direction of the press cover, there is again an opposing flexion. This deformation of the press cover on entry and exit is also referred to as cycling nip. It is readily apparent that the tendency of the press cover to break particularly at this point is very high by virtue of the high mechanical stress. Correspondingly, there are many known measures from the prior art that are intended to increase the stability of the press cover.

The press cover must thus have sufficient flexibility in order that it can be guided around the shoe, it must be sufficiently stiff in order that it does not become too significantly deformed or compressed in the nip under the press load, and it must be sufficiently welding-resistant. Press covers therefore consist of a single- or multi-ply polymer layer, preferably of polyurethane, into which reinforcing fibers may be embedded in the form of nonwoven scrims or woven fabrics.

The present invention relates to such articles of the generic type that have been specified at the outset.

Multilayer press covers known from the prior art, when used as intended, have a tendency to premature failure as a result of detachment—often only local—of one of the polymer layers. In practice, this leads to unplanned stoppages of the press apparatus and hence to extended, costly shutdown times.

Press covers of the generic type have become known inter alia from US 2009/0038770 A1 and DE 102015217941 A1.

It is accordingly an object of the invention to specify a press cover, that avoids the disadvantages of the prior art. More particularly, detachment of the individual polymer layers is to be avoided, the lifetime of such a press cover is to be increased, and the stoppage periods of a press apparatus equipped with such a press cover are to be reduced.

The object is achieved by the features of the independent claims. Particularly preferred and advantageous embodiments of the invention are given in the dependent claims.

The inventors have recognized that detachment of the individual polymer layers can be avoided when the individual polymer layers are matched exactly to one another. This is the case when the thickness of the radially outermost polymer layer of a multilayer press cover in total is between at least 5% and at most 60%, preferably at most 55%, of the total thickness of the press cover, i.e. the thickness of all polymer layers. The values mentioned are meant inclusively. Even though it has not been possible to conclusively elucidate the mechanism of action, the inventors have noticed that, in the case of such a thickness ratio, it is possible to specify a press cover that has a particularly low tendency of the individual polymer layers to delaminate in the operation of the press. This finding is independent at first of the material used in the press cover.

The advantages of the invention are achieved particularly satisfactorily when, in addition to the said thickness ratio of the radially outermost polymer layer in relation to the overall press cover, grooves or holes are also provided in the radially outermost polymer layer. This is particularly true when a particular ratio of the depth of such grooves or holes in relation to the thickness of the radially outermost polymer layer is chosen. For instance, the depth of the grooves or holes may be at least 35%, preferably at least 50%, and at most 95% of the thickness of the radially outermost polymer layer.

In addition, the inventors have recognized that, in addition to the two measures of the thickness ratio and depth ratio, delamination can be prevented by making the first and second polymer layer different with regard to their hardness. A difference of 1 to 6 Shore is sufficient here, namely when the second polymer layer is made to be less hard than the first polymer layer.

If reference is made to thickness or depth in the present invention, this means the greatest spatial extent which is measured in radial direction, i.e. perpendicular to the longitudinal axis of the press cover. Total thickness, viewed in a cross section perpendicular to the longitudinal axis of the press cover, is the perpendicular distance between the radially outermost and radially innermost shell surface thereof.

The advantages of the invention are achieved particularly efficiently when polyurethane is used with preference, as in the case of a press cover as claimed in any of claims 6 to 8.

If it is said in the invention that something has been manufactured from a substance, what this means is that it has been produced partly or entirely from such a substance.

In the context of the invention, a press apparatus means, for example, a shoe press, for example for dewatering or treatment, such as smoothing, of a fibrous material web. The shoe press comprises a shoe press roll and an opposing roll that together form or bound a press nip. The shoe press roll further comprises a circumferential press cover and a fixed press element, called the press shoe. The latter rests on a supporting, likewise stationary yoke—for example via hydraulic press elements—and is pressed onto the circumferential press cover. The press cover revolves relative to the fixed press shoe and yoke and is thus pressed onto the opposing roll in the press nip. Press shoe and yoke are arranged radially within the press cover. The term “fixed” is understood to mean that the press element does not revolve relative to the shoe press roll or the opposing roll, but can move in a translational manner—toward and away from the opposing roll, preferably in radial direction thereof—and hence relative to the opposing roll. In addition to the fibrous material web and the press cover, it is possible for one or more continuously circumferential press felts and/or further continuously circumferential press belts to be guided through the press nip of the shoe press. Such a shoe press may of course comprise more than one press nip.

A fibrous material web in the context of the invention is understood to mean a laid scrim or unstructured tangle of fibers, such as wood fibers, plastic fibers, glass fibers, carbon fibers, additions, additives or the like. For example, the fibrous material web may take the form of a paper, cardboard or tissue web. It may essentially comprise wood fibers, where small amounts of other fibers or else additions and additives may be present. This is a matter for the person skilled in the art according to the individual use.

A press cover in the context of the invention is understood to mean a belt, hose or cover which, as described, is guided together with a fibrous material web through the press nip of a shoe press. The fibrous material web can be dewatered in operation as intended by contacting the radially outermost surface (polymer layer) of the press cover with a press felt that directly bears the fibrous material web to be dewatered. According to the embodiment of the press device, for example for smoothing thereof, the press cover in operation as intended may also come into direct contact with the fibrous material web. The press cover is in the form here of a continuous cover (hose) which is endless in circumferential direction about its longitudinal axis. At its axial ends—viewed in breadth direction (along the longitudinal axis)—it is open. It is thus possible for the press cover to be held by two lateral tension plates at its axial ends, in order to form the shoe press roll. Rather than being guided by the two lateral tension plates, the press cover, as is the case for open shoe presses, may be guided over the press shoe and multiple guide rolls. Irrespective of whether the press cover is guided by the tension plates or the guide rolls, the press shoe (or the guide rolls) come(s) (intermittently) into contact with part of the radially innermost surface of the press cover. The radially outermost surface of such a press cover, i.e., for example, the radially outermost polymer layer thereof, may have been provided with grooves and/or blind holes.

The press cover may have been partly or completely manufactured from a polymer. The polymer used may be a castable, curable, preferably elastomeric, polymer such as polyurethane. The polymer may consequently be formulated as a cast elastomer.

“Polymer layer” means a layer that comprises or has been produced entirely from such a castable, curable, preferably elastomeric, polymer. The polymer layer may preferably be a cured layer that has been produced in one piece by primary shaping. In other words, it has been made by primary shaping in monolithic form, i.e., for example, by casting. The term “one-piece” also includes cases in which one layer has in turn been produced from multiple strata of the same material in the casting of the polymer. However, this is only true if these strata are essentially no longer visible after the curing, and the result is instead a single, preferably uniform layer. The same is correspondingly true of the finished press cover.

In the case of provision of multiple polymer layers, these may be arranged one on top of another viewed in radial direction—at least in sections over the width of the press cover. “At least in sections over the width of the press cover” means that the press cover has only a single layer, for example at its axial ends, whereas it is in two-layer or multilayer form between the axial ends. However, the polymer layers may also extend over the entire width of the press cover. It is also possible for the thickness of the press cover—and hence the thickness of the individual polymer layers—to vary in sections over the longitudinal axis in a section through the longitudinal axis thereof. For example, the radially outermost polymer layer in the region of the widthwise edges of the press cover may be lower than in the middle of the press cover. In other words, in the region of the widthwise edges, the radially outermost polymer layer may be less thick than a radially inner or radially innermost polymer layer. Preferably, exactly one, two or three polymer layer(s) is/are provided. These may be in identical form in terms of their polymer or may vary in terms of their hardness or stoichiometry of the prepolymer. A total thickness of the finished press cover in a section through the longitudinal axis thereof, measured in radial direction, may be 5 to 10 mm, preferably 5 to 7, more preferably 5 to 6 mm. According to the invention, in the case of provision of a single layer, the press cover may have been manufactured from just one casting, i.e. in monolithic form, such that the single layer has the thickness just mentioned.

A finished press cover in the context of the invention is one wherein the at least one polymer layer has been cured and possibly finally processed, i.e. is ready for use for the purpose stated at the outset, in a shoe press for example. Analogously, “finished polymer layer” means a layer that has been cured.

In principle, it is conceivable that the press cover has a reinforcing structure. The term “reinforcing structure” in the context of the invention means a reinforcement of the at least one layer containing or consisting of the polymer—i.e. the polymer layer. The reinforcing structure may be entirely embedded here into the polymer layer, such that the reinforcing structure does not extend beyond the boundary of the polymer layer. In other words, the polymer layer assumes the role of a matrix that surrounds the reinforcing structure and binds to the matrix as a result of adhesion or cohesion forces. Such a reinforcing structure may include textile linear structures—e.g. yarns or twines—and/or textile fabrics—for example woven fabrics, loop-formed knitted fabrics, loop-drawn knitted fabrics, braids or scrims—and may be producible from a corresponding starting material, for example by winding. “Starting material” is understood to mean that material or semifinished product by means of which the reinforcing structure of the finished press cover of the invention is produced.

The basis for the expression “at most” based is meant to be a right-sidedly closed interval including all values between greater than zero and the maximum value specified (maximum value). What is meant, for example, by “at most 5” is thus the interval between (including or greater than) 0.01 and (including or exactly) 5.

The invention also relates to a press roll, such as shoe press roll, for a shoe press for dewatering of a fibrous material web, wherein the press roll includes at least one press cover of the invention.

The invention also relates to a shoe press for dewatering of a fibrous material web, preferably a paper, cardboard, tissue or pulp web, comprising a press roll and an opposing roll that together form or bound a nip, wherein the press roll comprises a circumferential press cover, wherein the press cover takes the form according to the invention.

The invention finally relates to the use of a press cover of the invention for a press, such as shoe press for dewatering of a fibrous material web, preferably a paper, cardboard, tissue or pulp web.

The invention is elucidated in detail hereinafter with reference to the drawings without restriction of generality. The drawings show:

FIG. 1 a schematic side view as a partial section of a shoe press with a press cover in a working example of the present invention.

FIGS. 2a and 2b embodiments of a press cover each in a section through its longitudinal axis;

FIG. 3 a highly schematic diagram of an apparatus for production of the press cover in a side view.

FIG. 1 shows, in a schematic side view as a partial section, a shoe press 10 which, in the present context, comprises a press roll of the invention, such as a shoe press roll 12, and an opposing roll 14. Shoe press roll 12 and opposing roll 14 are arranged parallel to one another with regard to their longitudinal axes. Together, they form or bound a nip 22.

While the opposing roll 14 here consists of a roll of cylindrical configuration that rotates about its longitudinal axis, the shoe press roll 12 is composed of a shoe 16, a stationary yoke 18 that bears it, and a press cover 20. Shoe 16 and yoke 18 are in a fixed arrangement in relation to the opposing roll 14 or the press cover 20. This means that they do not rotate. The shoe 16 is supported here by the yoke 18 and pressed onto the radially innermost surface of the press cover 20 that revolves relative thereto via hydraulic press elements (not shown). The press cover 20 that surrounds shoe 16 and yoke 18 in circumferential direction rotates here about its longitudinal axis in the opposite sense from the opposing roll 14. Owing to the concave configuration of the shoe 16 on its side facing the opposing roll 14, the result is a comparatively long nip 22.

The shoe press 10 is especially suitable for dewatering of fibrous material webs 24. In the operation of the shoe press, a fibrous material web 24 is guided through the press gap 22 with one or two press felts 26, 26′. In the present case, there are exactly two press felts 26, 26′ that accept the fibrous material web 24 between them in a sandwich-like manner. In the course of passage through the nip 22, the press felts 26, 26′ exert a pressure indirectly on the fibrous material web 24 in the nip 22. This is accomplished in that the radially outermost surface of the opposing roll 14 on the one hand and the radially outermost surface of the press cover 20 come into direct contact with the corresponding press felts 26, 26′. The liquid exiting from the fibrous material web 24 is temporarily absorbed by the press felt(s) 26, 26′ and any recesses provided in the press cover surface (not shown). After leaving the nip 22, the liquid absorbed by the depressions of the press cover 22 is spun off before the press cover 20 enters the press gap 22 again. In addition, the water absorbed by the press felt 26, 26′ can be removed by suction elements after departure from the press gap 22.

In a further embodiment of the invention, not shown in the figures, it is possible to dispense with the press felts 26, 26′. In such a case, the fibrous material web 24 is in direct contact first with the press cover 20 and secondly with the opposing roll 14, which together form a press nip. The latter may then be executed as a heated drying cylinder.

The press cover shown in FIG. 1 may, as shown in the figures that follow, be executed in accordance with the invention.

FIGS. 2a and 2b show different embodiments of the invention in a partially depicted cross section, not to scale, through the longitudinal axis 20′ of the finished press cover 20. The distance of the longitudinal axis 20′ from the radially innermost surface of the corresponding polymer layer of the press cover 20 is likewise not shown to scale.

According to FIG. 2a , exactly two polymer layers are provided, namely a first polymer layer 20.1 and a second polymer layer 20.2. In the present case, the first polymer layer 20.1 is simultaneously the radially outermost polymer layer of the press cover 20. By contrast, the second polymer layer 20.2 is simultaneously the radially innermost polymer layer of the press cover 20. Both polymer layers 20.1, 20.2 adjoin one another directly, viewed in radial direction, i.e. there is no interlayer between the two.

As shown, a reinforcing structure 20″ may have been provided in the second polymer layer 20.2. In the present case, a reinforcing structure 20″ has been embedded into the single polymer layer 20.1. This is indicated by the hatched circles that may be textile fabrics or linear structures such as fibers. The reinforcing structure 20″ has been completely embedded into the second polymer layer 20.2. This means that the reinforcing structure 20″ does not extend beyond the boundaries of the polymer layer 20.2.

In the present case, the first and a second polymer layer 20.1, 20.2 have been manufactured from a polyurethane. This is obtainable from a prepolymer and a crosslinker.

The thickness d of the first polymer layer 20.1—viewed in radial direction—according to the invention is less than half the total thickness D of the entire press cover 20, i.e. of the thickness of all polymer layers 20.1, 20.2 taken together.

FIG. 2b shows, in a modification from FIG. 2a , a three-layer press cover. This comprises a first polymer layer 20.1—the radially outermost here, a radially innermost, third polymer layer 20.3, and a second polymer layer 20.2 arranged between them in the manner of a sandwich. The arrangement—as also in the diagram of FIG. 2a —is viewed proceeding from the longitudinal axis 20′ of the press cover 20 in radial direction thereof. In the present case, a (single) reinforcing structure 20″ is provided merely in the second polymer layer 20.2. Of course, this might not be the case, and so such a reinforcing structure 20″ could alternatively or additionally also be disposed in the first polymer layer 20.1 and/or the third polymer layer 20.3. Here too, the first and second polymer layer 20.1, 20.2 have each been produced from or comprise a polyurethane. These statements are also analogously applicable to FIG. 2a . By virtue of the choice of the inventive thickness ratio of the thickness d of the first polymer layer 20.1 in relation to the total thickness D of the press cover 20 here too, the result is a press cover with which detachment of the individual polymer layers from one another is avoided.

FIG. 3 shows, in a highly schematic side view, an apparatus for production of a press cover 20 of the invention. The apparatus in the present context has exactly one cylindrical winding mandrel 4, with application here, for example, of a starting material 20′″ in spiral form to the radially outermost cover surface thereof. After being embedded into the polymer, the starting material 20″″ forms the reinforcing structure 20″ of the finished press cover 20 of the invention.

The diagram shows an initial stage of the production process. In the present case, for this purpose, one end of the starting material 20′″ has been secured to a polymer disposed at the outer extent of the winding mandrel 4. Apart from the schematic diagram shown, it would also be possible for one end of the starting material 20′″ to lie on or have been applied to the winding mandrel 4, i.e. directly, without initial provision of a polymer between starting material 20′″ and winding mandrel 4. The starting material 20′″ here may be a textile fabric or linear structure.

The winding mandrel 4 is mounted so as to be rotatable about its longitudinal axis 20′, which corresponds to the longitudinal axis of the press cover to be produced. Longitudinal axis 20′ runs at right angles here into the plane of the drawing. A casting material, such as castable, curable elastomeric polymer, e.g. polyurethane, is applied via a conduit 5 through a casting nozzle 6 downward onto the radially outermost cover surface of the winding mandrel 4 or onto the starting material 20′″. Such a casting material may be chosen, for example, with respect to its pot life and viscosity such that it does not drip off the winding mandrel 4 in the course of casting. During this period, the winding mandrel 4 is rotated about its longitudinal axis in the direction of the arrow. Simultaneously with this rotation, the casting nozzle 6 is guided parallel to and along the longitudinal axis 20′ relative to the winding mandrel 4 by means of a suitable guide (not shown in detail in FIG. 3). Simultaneously with the casting application of the casting material, the starting material 20′″ is unrolled and wound on the rotating winding mandrel 4 to give windings. It is possible here for the casting material to get through the starting material 20′″ through to the winding mandrel 4. The polymer in this example, after the curing step, forms a radially innermost and preferably elastomeric polymer layer corresponding to the polymer layer 20.2 of the press cover of FIG. 2a , of which FIG. 3 shows just part.

The casting material exiting from the casting nozzle 6 is a mixture of a prepolymer and a crosslinker. The former is provided from a prepolymer vessel (not shown) in which it is stored or stirred up. The prepolymer may comprise an isocyanate of the invention and a polyol. It may be present in the prepolymer vessel, for example, in the form of a prepolymer of the substances just mentioned.

The crosslinker may be provided in a crosslinker vessel. It is executed in accordance with the invention.

Prepolymer vessel and crosslinker vessel are assigned to the apparatus for production of a press cover 20. They are connected via conduits (likewise not shown) in a flow-conducting manner to a mixing chamber (not shown) connected upstream of the casting nozzle 6 in flow direction. The prepolymer/crosslinker mixture is thus produced upstream of and outside the casting nozzle 6, i.e. mixed in the mixing chamber. Irrespective of the production of the mixture, this is then applied to the surface of the winding mandrel 4 to form the at least one polymer layer of the press cover 20.

By means of such a continuous casting operation, which is also known as rotary casting, a continuous press cover 20 that forms an intrinsically closed cylinder about its longitudinal axis 20′ is thus gradually produced over the width of the winding mandrel 4, the internal circumference of which corresponds essentially to the outer circumference of the winding mandrel 4.

In principle, it would be conceivable to wind the starting material 20′″ onto more than one winding mandrel 4 shown in FIG. 3. For example, it would be possible to provide two winding mandrels that could be arranged in parallel at a distance from one another with regard to their longitudinal axes. Alternatively, it would also be conceivable to apply the polymer to the radially inner cover surface of the winding mandrel 4 as well, for example in the manner of spinning. Irrespective of the embodiment addressed, the finished press cover 20 is finally removed from the at least one winding mandrel 4.

As shown in FIG. 3, the press cover 20 takes the form according to the invention.

Although this is not shown in the figures, the reinforcing structure 20″ of the at least one polymer layer 20.1, 20.2 may also have been constructed from multiple starting materials 20′″ that have been placed one on top of another in radial direction and each run in longitudinal axis direction and in circumferential direction of the press cover 20. 

1-14. (canceled)
 15. A press cover (20), band, hose or jacket to be guided together with a fibrous material web through a press nip of a shoe press, the press cover comprising: a first polymer layer (20.1) being a radially outermost polymer layer of the press cover (20) relative to a longitudinal axis (20′) of the press cover (20), said first polymer layer (20.1) having a thickness of not more than 60% of a total thickness of the press cover (20) in a radial direction of the press cover (20), said first polymer layer (20.1) having a radially outermost shell surface and grooves or holes introduced into said radially outermost shell surface, said grooves or holes having a depth in the radial direction of the press cover (20) of at most 95% of a thickness of said first polymer layer (20.1); a second polymer layer (20.2) being a radially innermost polymer layer relative to the longitudinal axis (20′) of the press cover (20); said first and second polymer layers (20.1, 20.2) each including or being formed from a polyurethane, and said polyurethane being formed from a prepolymer and a crosslinker; said prepolymer of said first polymer layer (20.1) being a reaction product of: phenylene 1,4-diisocyanate (PPDI), naphthalene 1,5-diisocyanate (NDI) or 3,3′-dimethyl-4,4′-biphenylene diisocyanate (TODI) and at least one polyol selected from a polyether polyol, a polycarbonate polyol, a polyether polycarbonate polyol, or diphenylmethane 4,4′-diisocyanate (MDI) and at least one polyol selected from a polycarbonate polyol, a polyether polycarbonate polyol, or mixtures thereof; said prepolymer of said second polymer layer (20.2) being a reaction product of: diphenylmethane 4,4′-diisocyanate (MDI), toluene 2,4-diisocyanate (TDI) or naphthalene 1,5-diisocyanate (NDI) and at least one polyol selected from a polyether polyol, or mixtures thereof; and said crosslinker including butane-1,4-diol (BDO), hydroquinone 1,4-bis(2-hydroxyethyl) ether (HQEE), 4,4′-methylenebis(3-chloro-2,6-diethylaniline) (MCDEA), diethyltoluenediamine (DETDA), dimethylthiotoluenediamine (DMTDA) or mixtures thereof.
 16. The press cover (20) according to claim 15, wherein said thickness of said first polymer layer (20.1) corresponds to at least 5% of the total thickness of the press cover (20).
 17. The press cover (20) according to claim 15, wherein said thickness of said first polymer layer (20.1) corresponds to at most 55% of the total thickness of the press cover (20).
 18. The press cover (20) according to claim 15, wherein said depth of said grooves or holes corresponds to at least 35% of said thickness of said first polymer layer (20.1).
 19. The press cover (20) according to claim 15, wherein said depth of said grooves or holes corresponds to at least 50% of said thickness of said first polymer layer (20.1).
 20. The press cover (20) according to claim 15, wherein said first and second polymer layers (20.1, 20.2) adjoin one another in the radial direction of the press cover (20).
 21. The press cover (20) according to claim 15, wherein said first polymer layer (20.1) has a Shore A hardness of between 90 and
 98. 22. The press cover (20) according to claim 15, wherein said second polymer layer (20.2) has a Shore A hardness of between 90 and
 96. 23. The press cover (20) according to claim 15, wherein said first and second polymer layers (20.1, 20.2) have a Shore A hardness differing by between 1 and 6, and said second polymer layer (20.2) is less hard than said first polymer layer (20.1).
 24. A press roll or shoe press roll (12) for a shoe press (10) for treatment of a fibrous material web (24), the press roll or shoe press roll (12) comprising at least one press cover (20) according to claim
 15. 25. A shoe press (10) for treatment of a fibrous material web (24), a paper web, a cardboard web, a tissue web or a pulp web, the shoe press (10) comprising: a press roll or shoe press roll (12) and an opposing roll (14) together forming or bounding a nip (22); said press roll or shoe press roll (12) including a circumferential press cover according to claim
 15. 26. A method of using a press cover (20) for a press or shoe press (10), the method comprising the following steps: treating a fibrous material web (24), a paper web, a cardboard web, a tissue web or a pulp web by using the press cover (20) according to claim
 15. 